3rd Grade Math: Numbers with Decimals

Learning Decimals

What Are Decimals?

Decimals represent numerical amounts that are less than one. You may not realize it, but every time you buy an item, you are dealing with decimals. Let's say you buy a piece of candy for 99 cents. You can write 99 cents as a decimal like this: $0.99. Similarly, if you buy a bottle of juice for $2.50, you're still working with decimals because you're paying two whole dollars and then 50 cents ($0.50) of another dollar.

What Are Fractions?

Fractions and decimals give you two different ways of writing the same numbers. For example, 'four-tenths' can be written as 0.4 or 4/10. Similarly, 'eighty-eight hundredths' can be written as 88/100 or .88.

Both fractions and decimals can be understood as part of a whole number. If you have a pizza divided into six slices, and you eat two, you have eaten 2/6 of the pizza. In other words, you have eaten a part of the whole. The fraction 2/6 is the same as 1/3, because you can make three groups of two slices each. You can also write 1/3 in decimal form, as 0.33.

Decimal Addition

Eventually, you will learn how to add numbers with decimal points. Although you likely won't encounter this until 4th grade, you have actually already added and subtracted decimal amounts because you learned to add and subtract money.

The total price for milk and a loaf of bread might be $2.75 + $3.05. To calculate, write the 2.75 over the 3.05. Then, carry the decimal point down so that it is under the addition problem, but still lines up with the decimals in 2.75 and 3.05. Finally, add the numbers. The answer is $5.80.

If one number is whole (like 3 or 20) and the other one is a decimal, you can add them by writing point zero after the whole number. For example, three would become 3.0, and 20 would become 20.0. This makes it easier to line up the decimal points.

You can use a sales receipt for practice adding decimals. Ask your parent for a grocery store receipt. Fold over the bottom of the receipt so you can't see the total. Add the numbers on a separate piece of paper and check your answer by looking at the receipt total when you're done. Below are some sample problems with answers to demonstrate adding with decimals.